1036 Dynamic Theory. 



one and seven. The valence of sulphur towards hydrogen is constant, but 

 towards oxygen and towards hydrogen and oxygen varies from four to 

 six, and towards chlorine from two to four. " 



Different sorts of bodies are very differently affected by the same 

 temperature. A temperature low enough would make every body a 

 solid, and one high enough would make every one a gas. At the ordi- 

 nary temperature as observed by Gage, every solid may be regarded as 

 frozen matter, every liquid as melted, and every gas as matter in a state 

 of vapor. Air, that is oxygen and nitrogen have been frozen under a 

 great pressure, and alcohol has been frozen. 



We thus reach the conception that these different states of bodies are 

 due to, and are an indication of different degrees of energy that have 

 been expended upon them. When the earth was first formed, so much 

 energ}' had been expended upon it that it was all in a state of incan- 

 descent gas. A great part of that energy has been radiated away, and 

 that which remains of it affects chiefly the interior of the earth, which 

 is still, no doubt, in a molten state. But the condition of bodies on 

 the earth's surface is largely determined by the action of the sun. If 

 it were not for that, all the water on earth would soon be ice, and even 

 the air would be frozen into chunks. The water is mostly fluid and 

 partty vaporous, and the air is gaseous, because the sun's energies 

 drive the molecules of these bodies apart, and it is by a constant exer- 

 tion of these energies that they are kept in the same average state from 

 age to age. We are to understand then that a body is solid because its 

 particles or molecules are comparatively close together; although in the 

 most solid of bodies the spaces are of far greater extent than the mole- 

 cules of the body. The reason that the spaces are as large as the}' are 

 is that the energy applied to the body sets up a motion among its mole- 

 cules, and they, by their activity, drive each other apart to distances cor- 

 responding with the degree of energy of their movements. In liquids the 

 activity of the molecules is greater, and the intermolecular spaces nre 

 greater. In gases the activity of the molecules is still greater and the 

 spaces still larger. It is estimated that the spaces in a gas are 1,000 

 times more extensive than the mass of particles of the gas. These spaces 

 increase with the temperature, and the temperature is likewise a meas- 

 ure of the outward pressure of a gas, and the pressure is due in turn to 

 the velocity of the movement of the particles or molecules. This ve- 

 locity is very great and it has been calculated for a number of gases. 

 At zero centigrade the velocity of ox}^gen molecules is reckoned at 

 1,512 feet per second, nitrogen 1,614, hydrogen 6,048. When the tem- 

 perature is reduced nearly to that at which these gases are liquified, 

 these molecular velocities are considerably reduced, but are still great. 

 For oxygen at 119c the velocity is 1,135 feet per second, nitrogen at 



